Each person decides for themself if they believe it is ok to cheat. In fact every decision anyone makes they "find" a way to justify their actions.
There is no clear way to know (exactly) who cheats more men/women. It has always been assumed that men are far more likely to cheat than women. However shows such as "Cheaters" and The Maury Povich Show (aka) "You are NOT the father!" has indicated that men don't exactly have a monopoly on cheating. Statistics/surveys are skewed based upon who is willing to (admit) they cheated and who has gotten (caught) cheating.
There are 3 bacis types of chearters. (1) The Incessant Cheater. This is someone who has probably never had a monogamus relationship in their life. They usually have magnectic personalities, flirt a lot, and bore fairly easily. They are always looking for a "new adventure".
(2) The Unbelieveable Opportunity Cheater. This is someone who may not be "planning" to cheat but the stars aligned just right where an opportunity presents itself to be with someone hot, out of their league, or someone they've had a secret crush/fantasy about. These types of cheaters often feel guilty afterwards and have been known to tell their partners to get the guilt out of their system.
(3) The Discontented Cheater. Of the 3 basic types of cheaters this is the one who actually feels “justified” on some level. He/she sees their cheating as being the result of something their mate is not doing for them….(sexually, showing appreciation, respect, admiration, or their mate complains more than compliments and they feel taken for granted. Bottom line in his/her mind is they are “reacting” to how they are being treated.
Most cheaters are looking to hold onto all that is good in their primary relationship while addressing their other wants/needs on the side.
An unhappily married man is far more likely to cheat than run to the courthouse and file for a divorce. It's been reported that women file for divorce 66% or 2/3rds of the time. That probably sheds some light on how the two genders deal with issues in a marriage.